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w. P. PLACE mm. srs'rm Filed Aug. 3, 1938 6 Sheets-Sheet G Approach 3532420114! Electmmotiveme Currenl' ww m fl u wu q n A JM m um 8 Q v H w 7 :Hfl--- n Patented Apr. 16, 1940 UNITED STATES SIGNAL SYSTEM Willard P. ,Place, Wilkinsburg, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application August 3, 1938, Serial No. 222,883

13 Claims.

My invention relates to signal systems, and more particularly to signal systems for railways.

I shall describe several forms of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

A feature of my invention is the provision in signal systems of the type here contemplated of novel and improved means effectively responsive to recurrent impulses of current. Another feature l of my invention is the provision of novel and improved means for restoring an electron tube of the controlled ionization type to a normal nonconductive condition subsequent to an impulse of electromotive force which renders the tube con- Again, a feature of my, invention is the provision in such signal systems of automatic switching means for selectively rendering active one or the other of two receiving means operating in parallel, one of such receiving means being selectively responsive to code impulses of direct current and the other being selectively responsive to coded alternating current. Other features and advantages of my invention will appear as the specification progresses.

, In the accompanying drawings, Figs. 1 and 2 are diagrammatic views of trackway apparatus and train-carried apparatus, respectively, of one form of apparatus embodying my invention when applied to a three indication signal system for railways. Fig. 3 is a diagrammatic view of a modified form of the train-carried apparatus of Fig. 2, and which also embodies my invention. Figs. 4 and 5 are d agrammatic views of trackway apparatus and train-carried apparatus, respectively, of another form of apparatus embodying my invention when applied to a four indication signal system for railways. Figs. 6, 7, 8 and 9 are diagrammatic views of different modifications of the train-carried apparatus of Fig. 5 and each ofresponsive to coded alternating current. Fig. 14 is a diagram illustrating the different code impulses supplied by the trackway apparatus of Fig. 1 and Fig. 4. Figs. 15 and 16 are diagrams illustrating operating characteristics of the train- 5 carried apparatus of Figs. 2, 3, 5, 6, 7, 8, 9, 10, 11, 12 and 13. Fig. 17 is a diagram illustrating an operating characteristic of the trackway apparatus of Fig. 4.

In each of the several views like reference char- 0 acters are used to designate similar parts.

It is to be understood, of course, that I do not wish to limit my invention to signal systems for railways, and this one application will serve to illustrate the many places where apparatus em- 15 bodying the invention will be useful.

Referring to Fig. l, the reference characters la and lb designate the track rails of a stretch of railway over which traffic normally moves from right to left as indicated by an arrow, and 20 which rails are formed by the usual insulated rail joints into consecutive track sections of which only one section -WX and the adjoining ends of thetwo adjacent sections are shown for the sake of simplicity. Each track section is provided with a track circuit comprising the track rails, means for supplying code impulses of direct current connected across the rails at the exit end of the section, and a code responsive relay means connected across the rails at the entrance of the section. Thus the source of current impulses for the track circuit of section W-X and the code responsive relay means for the track circuit for the section to the left, that is. the track section next in advance of section WX, are located adjacent the junction W of these two track sections. The means for supplying such code impulses of direct current to the track circuit of section W-X is governed by the relay means for the track circuit for the section next in advance,

and comprises a battery 2, a code transmitter CT and a track transformer or reactor TI.

The code transmitter C'I comprises a pair of slow acting relays RI and R2 which are energized from a suitable source of current having terminals B and C. Relay RI controls the energization of relay R2 over a front contact, and relay R2 controls the energization of relay RI over a back contact-in a manner which is obvious from the drawing. Consequently, as long as current continues to be supplied from the source BC, relays RI and R2 will continue to operate at a rate which is determined by the retardation period of these two relays. In this manner, intermittent-or coding operations of a contact finger I 5 of relay RI are obtained, the contact finger I being the front contact member of a continuity transfer type of contact. Obviously, the two relays RI and R2 can be replaced by any suitable type of code transmitter, the essential requirement being that the contact finger 3 operates periodically at a desired rate. The rate may, for the purposes of illustration, be assumed to be of the order of 60 times per minute.

A portion of the winding 4 of transformer TI is connected with the rails of section W-X over wires 5 and 6, contact finger 3 and the transfer contact I being interposed in wire 6. The full winding 4 of transformer TI is connected with battery 2 over back contact 8 and transfer contact l of relay RI, and contact fingers of relays WS! and WS2 of the code responsive relay means of the track circuit of the section next in advance 'of section W-X. At such time as relay WSI is picked up closing its front contacts 9 and ID; or relay WSI is released closing its back contacts II and I2, and relay WS2 is picked up closing front contacts l3 and I4, the positive terminal of battery 2 is connected with the lefthand terminal of winding 4 and the negative terminal of battery 2 is connected with the righthand terminal of winding l. Again, when relay SI is released to close back contacts II and I2, and relay WS2 is released to close its back contacts i5 and IS, the connection of battery 2 with the winding 4 is reversed as will be apparent by an inspection of Fig. 1.

It follows that under clear traffic conditions in advance of section WX so that relay WSI is picked up in a manner to later appear, or under approach traffic conditions in advance so that relay WSI is released and relay WS2 is picked up as will later appear, recurrent impulses of direct current of positive polarity are supplied to the track circuit of section WX to effect clear tion W-X to effect approach trafllc conditions for that section. The trackway apparatus thus far described in Fig. 1 is similar to that described and claimed in the copending application for United States Letters Patent, Serial No. 60,240, filed January 22, 1936, by W; P. Place and A. J. Sorensen, for Railway signaling apparatus. As

fully explained in the aforementioned application Serial No. 60,240, each time the contactl-S of relay RI is closed energy is stored in the magnetic circuit of the transformer TI, and each time the contact l8 is opened and contact 2-! is closed, the magnetic energy rapidly collapses and causes to flow in the track circuit of section W--X a relatively short current impulse having a relatively high peak voltage, the polarity of the impulse being governed by the position of the relays WS! and WS2 associated with the track circuit of the section .next in advance. Referring to Fig. 14, such relatively short high peak voltage impulses are represented by the center and lower diagrams, the center diagram indicating that the impulses are of positive polarity and the lower diagram indicating that the impulses are of negative polarity. However, it is to be noted that in the form of the invention disclosed by Figs. 1, 2 and 3, recurrent impulses of positive polarity are used to reflect clear traffic conditions in advance, recurrent impulses of negative polarity are used to reflect approach'trafllc conditions in advance, and no such current impulses reflect the stop or slow speed traffic conditions.

Referring again to Fig. 1, the code responsive relay means for the track circuit of section W-X includes two code following relays XTRI and XTR2, which are connected across the track rails in parallel and are made selectively responsive to the polarity of the track circuit current impulses by asymmetric units IT and IS, the unit I! being disposed to pass only current impulses of positive polarity to relay XIRl and unit l8 being disposed to pass only current impulses of negative polarity to the relay XTR2. The relay XTRI controls over front contact I8 a slow release repeater relay XSI and the relay XTRZ controls over front contact 20 a slow release repeater relay XS2. Thus when recurrent impulses of positive polarity are supplied to the track circuit of section WX, the relay XTRI is operated once for each impulse and the relay XSI is intermittently energized and is continuously picked up due to its slow release period being sufficient to retain relay XSI energized from one impulse to the next. Similarly, when current impulses of negative polarity are supplied to the track circuit of section WX, the relay XTR2 is operated and the relay XS2 is continuously picked up. When the section W--X is occupied and the track circuit is shunted both relays XTRI and XTRZ are inactive and both relays XSI and X82 are released at the end of their slow release periods.

' In Fig. 1, a wayside signal is provided for each section, the signals being here shown as of the three indication color light type. Looking at signal XS for section WX, the green lamp G is illuminated to display a clear signal when the track circuit for section W-X is supplied with current impulses of positive polarity and the relay XSI is picked up closing front contact 2|. When the track circuit for section W-X is supplied with current impulses of negative polarity so that relay X82 is picked up closing front contact 22, and relay XSI is released closing back contact 23 the yellow lamp Y at signal XS is illuminated to display an approach signal. When both relays XSI and X82 are released because the track section W--X is occupied the R. lamp of signal XS is illuminated over back contacts 23 and 24 to display a stop signal.

The relays XSI and X82 also control the supply of current to the track circuit for the section to the right of section W-X in the same manner as the relays WSI and WS2 control the current impulsessupplied to the track circuit of track section W-X. Furthermore, relays WSI and WS2 are controlled by the track circuit for the section next in advance of section W--X through the medium of code following relays WTRI and WTR2 in the same manner that relays XSI and X82 are controlled by the code following relays ml and XTR2. Also, the relays WSI and WSZ control the operating circuit for the signal WS in the same manner as the relays XSI and X82 control the operating circuit for the signal XS. It will be understood, of course, that each consecutive track section of the system is provided with trackway apparatus similar to that described in connection with the section W-X.

Referring to Fig. 2, the train-carried apparatus includes an inductor comprising two windings 25 and 26 mounted on the train in inductive relation with the track rails la and lb, respectively, and connected across a portion of the winding 21 of an input transformer T2. The connections of windings 25 and 25 are preferably such that the electromotive forces induced therein by current flowing in opposite directions in the rails Ia and lb add their effects. The winding 21 of transformer T2 is included in the grid circuit of an amplifier electron tube 28, the plate circuit of which tube includes a source of current 29 and the primary winding 30 of a coupling transformer T3. It is clear that electromotive forces induced in the windings 25 and 2 6 are amplified in the usual manner by the tube 28 and are reproduced in the winding 30 of the transformer T3 where they are effective to induce corresponding electromotive forces in the secondary winding 40 of transformer T3.

The train-carried apparatus is provided with two electron tubes GI and G2 of the controlled ionization type and each of which is provided anode 36, a filament or cathode 31 and a control.

grid 38. The filaments 34 and 31 are heated by a battery 33 in the usual manner. The grid of tube GI is connected with the upper outside terminal of the secondary winding of transformer T3, and the grid 38 of tube G2 is connected with the lower outside terminal of winding 40, a resistor 4| being preferably interposed in the connection to grid 35 and a resistor 42 being preferably interposed in the connection to grid 38. A center or mid terminal of winding 40 is connected with the filaments 34 and 31 over a resistor 43. A suitable source of direct current, such as a battery 3|, has its positive terminal connected through a resistor 32 with the anodes 33 and 36, the winding of a relay SRI being interposed between resistor 32 and anode 33 of tube GI, and the winding of a. relay SR2 being interposed between resistor 32 and the anode 36 of tube G2. The negative terminal of battery 3| is connected with the'filaments or cathodes 34 and 31 of the tubes by being connected between resistor 43 and the center terminal of winding 40. It is to be noted, therefore, that the tubes GI and G2 are connected in the so-called push-pull arrangement. A condenser CI is connected between the flla-. ments 34 and 31 and the terminal of resistor 32 common to the windings of both relays SRI and SR2. Theparts are so proportioned that the condenser CI and the inductance of the winding of relay SRI form an oscillatory circuit for the tube Gland the condenser CI and the inductance of the winding of relay SR2 form an oscillatory circuit for the tube G2. The condenser CI is preferably of relatively large capacity.

The parts are so proportioned that when no electromotive forces are applied to grids 35 and 38 through the transformer T3, the tubesGI and G2 are non-conducting, and the condenser CI is charged at a voltage substantially equal to that of battery 3|. Under. such non-conducting condition of tubes GI and G2 both relays SRI and SR2 are deenergi'zed and released. The relays SRI and SR2 are slow releasing in character and control the operating circuit of a'cab signal CS in a manner to shortly appear."

Assuming the train on which the apparatus of Fig. 2 is mounted enters the" track section W-X of Fig. 1 from the right under clear traiiic conditions in advance so that current impulses of current of positive polarity are supplied to the track circuit for" section W-X, electromotive forces are induced in the windings 25 and 25 by each such current impulse, such electromotive forces adding their .efiects. The resultant electromotive force is amplified by tube 28 and induces a corresponding electromotive force in winding 40 of transformer T3. The wave form of such induced electromotive force is substantially as illustrated by the first, third and fifth curves of Fig, 15 reading from the left, since the track circuit current impulses are all of positive polarity. That is to say, the wave form of the electromotive force induced in the winding 40 of transformer T3 in response to each current impulse of the track circuit comprises a first half cycle of positive polarity of relatively high peak voltage and a second cycle of negative polarity of a much lower peak voltage. The parts are so adjusted and connected that the electromotive force in duced in winding 40 in response to a track circuit current impulse of positive polarity causes during its first half cycle the upper terminal of winding 40 to be positive with respect to the lower terminal of winding 4|] with the result that the grid 35 of tube GI is rendered positive in potential with respect to cathode 34, and the grid 38 of tube G2 is rendered negative in potential with respect to its cathode 31. This positive potential of grid 35 with respect to the cathode 34 effects ionization for tube GI and tube GI becomes conductive, but tube G2 remains non-conductive due to the grid 38 being negative in potential with respect to cathode 31.

-When tube GI becomes conductive, condenser CI discharges through the oscillatory circuit consisting of the winding of relay SRI, anodecathode space of tube GI and back to condenser CI. This being an oscillatory circuit the current wave takes the form illustrated in Fig. 16, .the current rising to-a maximum value, dropping off to zero, and then tending to reverse and recharge the condenser at opposite polarity. The point 0 of Fig. 16 represents the point at which H tube GI becomes conductive, the point OX represents the point at which the flow of current from condenser CI is reduced to substantially zero due to the constants of 'the oscillatory circuit. The parts are so chosen that the time lapsing from point 0 to point OX is of the order of, say, onetenth second or suflicient for operation of a direct current relay of the usual type. When condenser CI begins to ioseits charge, current is supplied from battery 3| through resistor 32, winding of relay-SRI, anode-cathode space of "tube GI, resistor 43 and back to battery 3| The resistors' 32 and 43 and condenser CI are so proportioned that condenser CI on discharging supplies a substantial portion of the totalcurrent .with the result that when the oscillatory discharge from condenser CI falls to zero or at least to a relatively low value the. current flowing through tube GI falls to a value not suflicient to maintain the tube conductive, and the tube GI deionizes and becomes non-conductive. In other words, the over-discharge of condenser CI tends to force the anode of tube -GI negative giving the tube GI a chance to fully deionize.

It is to be noted that when tube GI becomes conductive the voltage of condenser CI is ex- 43 which establishes a negative grid bias for the tubes. This bias has no influence on the tube GI which is conductive but does serve to make it very difficult for tube G2 to ionize, so that during the immediately following or second half cycle of the electromotive force induced in the winding 40, and which half-cycle is of negative polarity so that the lower terminal of winding is positive with respect to the upper terminal of winding at, the tube G2 is maintained non-con ductive.

With tube GI rendered non-conductive the condenser Cl is quickly recharged so that the next impulse of track circuit current causes the above described operation to be repeated.

It follows that the relay SRI is periodically energized by the recurrent impulses of current produced in the anode circuit of tube GI in response to the recurrent impulses of current of the track circuit of section W-X. The relay SRI is slow releasing in character and remains picked up from one impulse to the next so that lamp G of the cab signal CS is steadily illuminated to display a clear signal by virtue of the circuit completed at front contact 4'! of relay SRI.

Assuming that when the train enters the track section WX approach traflic conditions in advance exist and recurrent impulses of current of negative polarity are supplied to the track circuit for section W-X, the wave form of the electromotive force induced in'winding 4D in response to each such track circuit current impulse of negative polarity is obviously opposite to that produced by the impulses of positive polarity and the wave forms are substantially as illustrated by the second, fourth and sixth curves of Fig. 15. This time, the lower terminal of winding 49. is first positive with respect to the upper terminal of the winding and the grid 33 of tube G2 is made positive in potential with respect to its filament 3? while the grid 35 of tube GI is made negative in potential with respect to its filament. Ionization is now effected in tube G2 and tube G2 is made conducting. Condenser CI discharges through the oscillatory circuit comprising winding of relay SR2 and the anode-cathode space of tube G2. The circuit constants for the circuits associated with tube G2 are the same as those for the circuits for tube GI and condenser CI provides a substantial portion of the anode current for tube G2 so that when the discharge of condenser CI falls to a relatively low value the current flowing through the tube G2 is insufiicient to maintain the tube conductive and the tube G2 deionizes and is restored to its normal non-conducting condition. The tube GI is maintained non-conducting during the second half cycle of the wave form of the induced electromotive force in substantially the same manner as tube G2 .is maintained non-conducting during the second half cycle of the wave form of the induced electromotive force when the track circuit current impulses are of positive polarity. Condenser CI is quickly recharged when the tube G2 is restored to its non-conducting condition and the operation is repeated on the next impulse of the track circuit current. Relay SR2 is thus intermittently energized in response to the track circuit current impulses of negative polarity and remains picked up from one impulse to the next due to its slow release characteristic. When relay SR2 picks up closing its front contact 48 and relay SRI is released closing its back contact 44, the yellow lamp Y of the cab signal CS is illuminated to display an approach signal. 7

In the event the track section W-X is already occupied by a train when the train on which the apparatus of Fig. 2 is mounted enters the section from the right, the first train shunts the track circuit current away from the second train and no electromotive forces are induced in the windings 25 and 26. The tubes GI and G2 are immediately restored to their non-conducting condition and relays SRI and SR2 are both released at the end of their slow release periods closing back contacts 44 and 45 so that the lamp R of the cab signal CS is illuminated to display a slow speed signal.

It is to be seen therefore that the apparatus in Fig. 2 is selectively responsive to recurrent impulses of direct current of positive and negative polarity through the medium of the tubes GI and G2. The condensr CI and its associated oscillatory circuit is effective to deionize the tube GI or G2, as the case may be, subsequent to each impulse of electromotive force that renders the tube GI or G2 conducting. Also, the condenser Ci and the anode circuit of either tube when made conductive so control the anode potential and the grid potential of the other tube that the latter tube is maintained non-conductive.

It is to .be noted that such relatively high peak voltage of track circuit current impulses causes, when the track rails are shunted by a train, high surges of current of many amperes for inducing electromotive forces in the train-carried inductor windings 25 and 26. It is possible therefore that "the stage of amplification including tube 28 will not be required, the tubes GI and G2 operating directly from the electromotive forces induced in the windings 25 and 26.

The train-carried apparatus of Fig. 3 is similar to that of Fig. 2 except a transformer T4 and a full-wave rectifier 49 are interposed between the winding of relay SRI and the anode circuit of tube GI, and a transformer T5 and a full-wave rectifier 50 are interposed between the winding of relay SR2 and the anode circuit of tube G2. The inductance of primary winding 5| of transformer T4 and the inductance of primary winding 52 of transformer T5 are in each case so proportioned that when a track circuit current impulse causes the tube GI or G2 to be conductive in the manner described in Fig. 2, the discharge of condenser CI of Fig, 3 takes the form of an oscillatory discharge and the tube GI or G2, as the case may be, is rendered non-conducting subsequent to each such impulse that causes the tube to be conductive. When the track circuit current impulses are of positive polarity and tube GI is rendered intermittently conductive, the recurrent impulses of current caused in the primary winding SI of transformer T4 induce electromotive forces in the secondary winding 53 of transformer T4 which when rectified by rectifier 49 are effective to energize the relay SRI. In a like fashion when tube G2 is rendered intermittently conductive in response to track circuit current impulses of negative polarity, the recurrent impulses of current flowing in the primary the train-carried apparatus of 'Fig. 3 is operated 'by the trackway apparatus of Fig. 1 in substantially the same manner as the apparatus of Fig. 2.

the lower left-hand portion of Fig. 4, the operat Referring to Fig. 4, the track rails la and lb of a stretch of railway over which traflic normally moves in the direction indicated by an arrow are formed by insulated rail joints into consecutive track sections the same as in Fig. 1, the section WX and the adjoining ends of the two adjacent sections only being shown in Fig. 4 for the sake of simplicity; Each track section is provided with a track circuit comprising the track rails, a source of recurrent code impulses of direct current and a code responsive relay means the same as in Fig. 1, except in Fig. 4 additional trackway apparatus is provided to supply at times impulses of current that are alternately positive and negative. As illustrated in Fig. 14, clear traflic conditions in advance of track section WX of Fig. 4 are reflected by current impulses alternately positive and negative in polarity, approach restricting traflic conditions are reflected by cur rent impulses of positive polarity, approach traffic conditions are reflected by current impulses of negative polarity, and stop or slow speed trafiic conditions are reflected y the absence of any such impulses. It should be noted that there are twice as many impulses per minute transmitted for clear traffic conditions as for either approach restricting or approach traflic conditions.

In Fig. 4, the code transmitter is modified to transfer from the supply of positive impulses of the approach restricting indication to the supply of negative impulses of the approach indication or vice versa in a specified sequence. Furthermore, as shown at the left-hand end of Fig. 4,

the code responsive relay means for the track circuit for the section next in advance of section WX includes code following relays ml and WTR2 and repeater relays WSI and W82, the same as in Fig. 1, and in addition a third repeater relay W83, the relay W83 being used to avoid undesirable signal flashing in changing from one indication to another.

Assuming at the start that the relays WSI, W82 and W83 are all deenergized and that clear traffic conditions exist for the section next in advance of section WX so that the current impulses supplied to the track circuit for the section next in advance are alternately positive and negative in polarity and the first impulse is one of positive polarity, the relay WTRI is operated and the relay WSI is energized. The next impulse is of negative polarity and relay WI'R2 is operated and relay W82 is energized, relay WSI remaining picked up by virtue of its slow release period. A condenser 55 is charged over a circuit including battery terminal B, back contact 56 of relay W83, and back contact 51 of relay WTRI, front contacts 58 and 59 of relays W82 and WSI, respectively, condenser 55 and terminal C.- The next. impulse of track circuit current is of positive polarity and relay WTRI is picked up to again energize relay WSI. The condenser 55 now discharges through a winding of relay W83 and relay W83 is picked up, the circuit including condenser 55, front contacts 53 and 58, front contact 60 of relay W'IRl, top winding of relay W83 and to condenser 55. From this point on relay W83 is maintained energized over a stick circuit including its lower winding and front contact GI, and front contacts 62 and 63 of relays WSI and W82, respectively. It follows that relay W83 is picked up only in response to three impulses of track circuit current of alternate polarity, but when picked upit remains picked up as long as the track circuit current impulses are alternate in polarity. As shown in ing circuits for a fourindication color light wayside signal WS for the section next in advance of section WX are governed by the relays WSI, W82 and W83. These operating circuits will be readily understood by an inspection of Fig. 4 and need not be described in detail since they form no part of my invention. This relay combination is similar to that disclosed and claimed in the copending United States application for Letters Patent Serial No. 217,944, filed July '7, 1938, by A. J. Sorensen. I

The code responsive relay means for the track circuit for section WX and for the other track circuits of the system are substantially the same as described in detail for the track circuit of the section next in advance of section WX.

The means for supplying code impulses of current to the track circuit for the section WX of Fig. 4comprises battery 2, track transformer Tl, a code transmitter CTI and two relays R3 and R4, relays R3 and R4 acting to pole change the connection of battery 2 with the winding 4 of transformer Tl in accordance with traffic conditions in advance. Relay R3 is controlled over a simple circuit including front contact 64 of relay WSI. Relay R4 is controlled by a pickup circuit including front contact 65 of relay W82 and a cam operated contact 66 of code transmitter CTI, and also over a stick circuit including its'own front contact 61 and two cam operated contacts 68 and 19 of the code transmitter in multiple as will shortly be described.

' Assuming the section next in advance of W-X is occupied so that both relays WSI and W82 section WX are of negative polarity to reflect approach trafllc conditions for the section WX. When approach traiflc conditions exist in advance and relay W82 is picked up closing front contact 65 the relay R4 is picked up in a manner to shortly appear. Battery 2 is now connected across winding 4 over front contacts 13 and 14 of relay R4 and the left-hand code contacts 15 and 16 of the code transmitter, the connection being opposite to that previously described so that the track circuit for section WX is now supplied with code impulses ofcurrent of positive polarity to reflect approach restricting traflic conditions for the section WX. When approach restricting traffic conditions exist in advance and relay WSI is picked up, the relay to supply the track circuit with impulses of positive polarity. Thus the track circuit of section WX, is now supplied with impulses of current alternately of positive and negativepolarity to reflect clear traflic conditions in the section WX. Again when clear tramc conditions exist in ad- Vance and both relays WSI and W82 are picked up to energize both relays R3 and R4, the battery 2 is reversibly connected across the winding 4 as will be evident from Fig. 4 so that impulses of current alternately of positive and negative polarity are supplied to the track circuit for section WX to reflect clear trafiic conditions.

In changing from approach restricting to approach or vice versa it is preferable to do so in a selected sequence so that the first impulse of reversed polarity appears in one-half of the usual cycle interval. If the time is extended to one and one-half cycle intervals a false signal flash may result. For example, if traffic conditions change from approach to approach restricting and relay R4 is energized and picked up at the instant the code transmitter CTI happens to be changing from the right-hand contacts H and T2 to the left-hand contacts 15' and I8 no effective impulse would be transmitted the first time lef -hand contacts l5 and I6 are closed, and there will be an interval of substantially one and one-half cycles before an impulse of positive polarity appears in the track circuit of section W-X. Again when trailic conditions change from approach restricting to approach it will be undesirable to release relay R4 when the code transmitter is changing from left-hand contacts 75 and it to the right-hand contacts II and '32, or no effective impulse would be supplied for an interval of substantially one and one-half cycle period. Such long delay between impulses is illustrated by the lower diagram of Fig. 17. To effect a proper sequence in the changing from approach restricting to approach condition or vice versa, as illustrated by the top diagram of Fig. 17, the code transmitter C'Ii is provided with cam operated contacts 68, 68 and I9, which function to allow relay R4 to pick up or release only during a particular part of the cycle of the code transmitter.

The code transmitter may be of any convenient type such, for example, as disclosed in the United States Letters Patent No. 1,913,826, granted June 13, 1933, to H. G. Blosser for Oscillating motors.

' It is sufficient for the instant application to say that as long as the current source whose terminals are E and C continues to supply current to the winding 80 of the code transmitter CTI the armature 8i is oscillated at a predetermined rate to alternately close the right-hand contacts 'II and I2 and the left-hand contacts 75 and I6, as well as to operate the cam operated contacts 66, 58, and I9 once for each cycle. Relay R4 is picked up over a circuit from terminal B, through winding of relay R4, front contact 65 of relay W52, cam operating contact 68 and terminal C, and contact 68 is closed only during that part of the cycle of the code transmitter CTI during which the right-hand contacts II and I2 are closed. Hence relay R4 can be-energized onlywhen the right-hand contacts TI and I2 are closed so that when on the next half cycle of the transmitter CTI the left-hand contests 75 and i8 are closed an impulse of current of positive polarity is supplied to the track circuit of section WX.

Relay R4 is retained energized over its stick circuit including terminal B, winding of relay R4, front contact 81 and cam operated contacts 68 and I9 in parallel. Thus if relay WSZ is released in response to a change in traflic conditions relay R4 is not released until such time as both contacts 68 and 79 are open. Contact I5 is directional and opens only on the swing to the right of each cycle, that is, during the instant the transfer is being made from righthand contacts 'II and I2 to left-hand contacts 15 and I6. Contact 68 is opened only during the interval the left-hand contacts 15 and 16 are open. It follows that relay R4 is released closing back contacts 69 and so that when the right-hand contacts II and I2 of the code transmitter are next closed an'impulse of current is supplied to the track circuit of section WX. It is to be seen, therefore, that with the code transmitter CT! constructed in the manner just described it is possible to transfer from approach restricting to approach or vice versa only during the proper instant in the operating cycle of the code transmitter. A condenser 82 may be connected across the winding 4 of the transformer TI to increase the peak voltage of the impulse, it being recalled that the impulses of direct current supplied to the track circuit are each of relatively short duration and of relatively high peak voltage. The means for supplying code impulses to each of the other track circuits of the system is substantially the same as just described in detail for the track circuit for section W-X.

The arrangement of a track transformer or reactance device including a winding mounted on a magnetic core and a condenser connected across such winding and the winding connected across the track rails for supplying current impulses to the associated track circuit when direct current supplied to such winding is interrupted is disclosed and claimed in my copending application Serial No. 239,523, filed November 8, 1938, for Signal systems.

Referring to Fig. 5, the train-carried apparatus adaptable of operation with the trackway apparatus of Fig. 4 includes two tubes GI and G2, the same as in Fig. 2. In Fig. 5 the primary winding 30 of the transformer T3 is connected directly with the windings 25 and 26 of the train-carried inductor, although a stage of amplification may be interposed in this connection if desired. The tubes GI and G2 operate the slow releasing relays S'RI and SR2 through code following relays CF I and CF2, respectively, relays SR! and SR2 functioning as slow acting repeater relays. Also, a third repeater'relay SR3 is provided for the train-carried apparatus for substantially the same reasonv as the relay W83 is included in the apparatus of Fig. 4. In Fig. 5, the generator 84 of a motor generator MG serves as the source of electrornotive force for the anode circuits of tubes GI and G2, the motor 85 of the motor generator MG being supplied with current from any convenient source such as the headlight generator whose terminals are 1332 and N32. The generator 84 whose terminals are designated B300 and N388 would, for example, supply a voltage of, say, 808 volts. In Fig. 5, an inductor L is connected in series with the condenser CI so that the oscillatory circuits associated with tubes GI and G2 comprise inductor L, condenser CI and the winding of relay CFI in the case of tube GI; and inductor L, condenser CI and the winding of relay CF! in the case of tube G2. Resistors 32 and 43 are interposed in the anode circuit the same as in Fig. 2, while two resistors I01 and I08 are connected with the grid circuits to provide a desired grid bias for the tubes from the source B32N32.

The repeater relay SRI is controlled over a front contact 86' of the code following relay CFI and the repeater relay SR2 is controlled over front contact 81 of the code following relay CF2. Repeater relay SR8 is controlled in substantially the same manner as relay W88 of Fig. 4. Starting with the relays SRI, SR2 and SR3 all deenergized and assuming that relay CFI is first operated closing front contact 88 to energize relay SRI, and then relay CF2 is operated closing front ccntact 81 to energize relay SR2, a condenser 88 is charged over a circuit from terminal B, back contact 89 of relay SR3, back contact 98 of relay CFI, front contacts 8| and 82 of relays SR2 and SRI, respectively, condenser 88 and terminal C. When relay CFI is next picked up closing its front contact 93 the condenser 88 discharges through the top winding of relay SR3 and that relay is picked up. Relay SR3 then remains energized as long as the relays SRI and SR2 remain picked up over the stick circuit including terminal B, front contact 88 of relay SR3, front contacts 95 and 86 of relays SRI and SR2, respectively, lower winding of relay SR3 and terminal C. s

In describing the operation of the apparatus of Figs. 4 and 5 Ishall assume that the train on which the apparatus of Fig. 5 is mounted enters track section WX of Fig. 4 from the right under clear traffic conditions so that the track circuit of section WX is supplied with recurrent impulses of current alternately positive and negative in polarity as illustrated by the top diagram of Fig. 14. I shall further assume that the train-carried relays are at the start all deenergized and the first track circuit current impulse is one of positive polarity so that the wave form of the electromotive force induced in the winding 40 of transformer T3 is substantially that illustrated by the first curve of Fig. 15 read ing from the left. During the first half cycle of such electromotive force the top terminal of winding 80 is positive with respect to the lower terminal and grid 35 of tube GI is rendered positive in potential with respect to its filament and tube GI ionizes and becomes conductive. With tube GI conductive, the condenser CI discharges through winding of relay CFI, anodefilament space of tube GI and inductor L. As explained in connection with Figs. 2 and 16 the discharge of condenser CI is oscillatory, the current rising to a. maximum and then decreasing and tending to reverse. When the current from condenser CI starts to decrease, current flows from the generator 84 through the anode circuit of tube GI and which circuit includes resistors 32 and 43 as well as the winding of relay CFI. As previously explained in connection with Fig.

2 the condenser CI supplies the'major portion of the current flowing in tube GI so that when the discharge from condenser CI falls to a relatively low value the current flowing through tube GI is insuflicient to maintain the tube ionized and the tube GI becomes deionized and is restored to its non-conductive condition. Furthermore, the tube G2 is maintained nonconducting during the second half cycle of this .rent produced in the anode circuit of tube GI operates the relay CFI and the repeater relay SRI is energized and picked up since the duration of the impulse flowing through tube GI is ofsufficient period to permit the relay SRI to pick up.

Condenser CI is quickly recharged subsequent to the restoring of tube GI to its non-conductive condition. The next impulse of track circuit current is of negative polarity and the electromotive force induced in the winding 40 has a wave form substantially-as illustrated by the second curve of Fig.- 15. As the lower terminal of winding 48 is first positive with respect to the upper terminal the grid 38 of tube G2 is made positive in potential with respect to its filament. Tube G2 is ionized and becomes conductive. The operation following the ionization of tube I G2 is substantially the same as that described in connection with tube GI except the code following relay CF2 is operated and the repeater relay SR2 is picked up. This time tube GI is maintained non-conductive during the second half cycle of the wave form in substantially the same manner as described in connection with Fig. 2. Condenser 88 is charged in response to the picking up of relays SRI and SR2 as previously explained. The next or third impulse of track circuit current is of positive polarity and tube GI is again made conductive so that relay CFI is operated to supply an energizing impulse to the relay SRI. With relay CFI picked up closing front contact 93 the condenser 88 discharges to pick up the relay SR3 as previously explained. From this point on the track circuit impulses alternately of positive and negative polarity cause the tubes GI and G2 to become alternately conductive and the relays CFI and CF2 to be alternately operated, the tubes GI and G2 being restored subsequent to each impulse through the medium of the condenser CI and its associated oscillatory circuits. Alternate operation of relays CFI and CF2 to periodically energize relays SRI and SR2 retains these relays picked up and the third repeater relay SR3 is energized and picked up over its stick circuit. The'relay SR3 controls over its front contacts 91 and 98 the circuits for the G lamp of the top group of lamps of the cab signal CS, and the R lamp of the bottom group of lamps so that the cab signal CS now displays a clear signal.

If approach restricting trafilc conditions exist for section WX when the train enters that section, the recurrent track circuit current impulses are of positive polarity as illustrated by the second diagram of Fig. 14. These recurrent track circuit current impulses of positive polarity cause operation of tube GI and relay CFI but tube G2 is maintained non-conductive and the relay CF2 is inactive. Relay SRI is now picked up but relay SR2 and relay SR3 are both released. Under this condition the Y lamp of the top group of lamps of signal CS is illuminated over back contact 39 of relay SR3 and'front contact "II of relay SRI, and the G lamp at the bottom group of lamps is illuminated over back contact Hill of relay SR3 and front contact I02 of relay SRI, so that the signal CS now displays an approach restricting signal.

If approach trafiic conditions exist for the section WX when the train enters that section so that the current impulses of the track circuit are of negative polarity as illustrated at the bottom diagram of Fig. 14, the electromotive forces induced in the winding 40 cause the tube leased. Under this condition of the relays the Y lamp of the top group of lamps is illuminated over back contacts 89 and I03 of relays SR3 and SRI, respectively, and front contact I of relay SR2, and the R lamp of the bottom group of lamps is illuminated over back contacts I00 and I04 of relays SR3 and SRI, with the result that an approach signal is displayed by the cab signal CS.

In the event the track section W-X is occupied by a first train then all track circuit current is shunted from the second train and both tubes GE and G2 remain nonconductive and both relays CPI and C32 are inactive so that all three relays SRI, SR2 and SR3 are released. Under this condition the lamp of the top group of lamps is illuminated over back contacts 99, I03 and I08, and the R lamp of the bottom group of lamps is illuminated over back contacts I00 and $84 so that the signal CS displays a slow speed cab signal.

in the form of the train-carried apparatus disclosed in Fig. 6, the windings and 26 are independent of one another, the winding 25 being connected with the grid circuit of tube GI and-the winding 28 being connected with the grid circuit of tube G2, as will be obvious from Fig. 6. The slow acting rela SRI is controlled by tube Gt through a transformer T4 and a full wave rectifier 2 i0, and the slow acting relay SR2 is controlled by tube G2 through a transformer T5 and a full wave rectifier III. A polar relay PR is provided, its right-hand Winding being serially interposed with the winding of relay SRI across the output terminals of rectifier H0, and

- its left-hand winding being serially interposed with the winding of relay SR2 across the output terminals of rectifier II I. The polar relay PR controls a slow acting relay SR4 through a transformer T8 in a manner to later appear. The cab signal CS5 is of the position light type capable of displaying four different indications. The oscillatory circuit associated with tube GI includes condenser CI, primary winding I I2 of the transformer T4, anode-cathode space of tube GI, and the winding of a relay R5 and an inductor LI in multiple. In a similar manner the oscillatory circuit for tube G2 includes condenser CI, primary winding N3 of transformer T5, anodefllament space of tube G2 and the winding of relay R5 and inductor LI in multiple. It will be understood that the inductor LI may be omitted and the winding of relay R5 proportioned to provide the desired inductance.

"in Fig. 6 a battery I23 is provided for heating the filaments of the tubes GI and G2 through resistor 43, resistor 43 being proportioned to provide a desired normal grid bias for the tubes.

Also, a resistor 108 is interposed between the terminal N300 of generator 84 and the resistor 43 and is thus, interposed in the anode circuits of the tubes. Normally the condenser CI is charged at substantially the voltage of the generator 84 the same as'in Fig. 5. I

In describing the operation of the apparatus of Fig. 6, I shall assume that a train on which the apparatus of Fig. 6 is mounted enters track section W--X of Fig. 4 under clear traflic conditions, the relays SRI, SR2, PR and SR4 being taken at the start as all deenergized. The windings 25 and 26 are so connected that the electromotive forces induced therein in response to a track circuit current impulse of positive polarity causes the grid 35 of tube GI to be first positive in potential with respect to its filament, and causes the grid 38 of-tube G2 to be first negative in potential with respect to its filament 31. Track circuit current impulses of negative polarity will therefore first cause the grid 38 of tube G2 to be positive with respect to its filament 31 and the grid 35 of the tube GI to be negative in potential with respect to its filament. As explained in connection with Fig. 2 the tube GI istherefore ionized and becomes conductive in response to a track circuit current impulse of positive polarity. The condenser CI discharges through the oscillatory circuit provided for tube GI. Current also flows from generator 84 through the anode circuit of tube GI. The circuit constants are so chosen that when the oscillatory discharge from condenser CI falls to substantially zero, tube GI deionizes and becomes non-conductive. The discharge of condenser CI and the bias voltage produced by the anode current from generator 84 flowing in resistors 43 and I09 maintain the tube G2 non-conductive during the second half cycle of the induced electromotive force in response to a track circuit current impulse of positive polarity in the same manner as described for Figs. 2 and 5. Furthermore, in Fig. 6 the relay R5 is momentarily picked up by the discharge of condenser CI and opens at its back contact II4 the connection of generator 84 with the anode circuits. The relay R5 will not ordinarily be needed; however, it provides additional means by which proper operation of the tubes GI and G2 is assured. The impulse of current flowing in the primary winding I I2 on transformer T4 when the tube GI is conductive causes an electromotive force to be induced in the secondary winding II5 of transformer T4 which when rectified by rectifier H0 is effective to energize relay SRI and the righthand winding of the polar relay PR, the relay SRI being picked up and the polar relay PR operating its polar contact members H8 and III to the right-hand position. The next current impulse of the track circuit is of negative polarity so that the tube G2 is ionized and becomes conductive while tube GI is maintained non-conductive. Condenser CI now discharges through the oscillatory circuit associated with tube G2 and the generator 84 functions to supply current to the anode circuit of tube G2, tube G2 deionizing and becoming non-conductive subsequent to the current impulseby virtue of the action of the condenser CI. This time the impulse of current produced in the primary winding II3 of transformer T5 induces an electromotive force in the secondary winding I I8 of that transformer which when rectified by rectifier I I I is effective to energize relay SR2 and the left-hand winding of relay PR, relay SR2 being picked up and relay PR operating its polar contacts II 6 and II! to their left-hand positions. From this point on the relays SRI, SR2 and PR are alternately energized in response to the track circuit current impulses, the relays SR2 and SRI being retained picked up due to their slow releasing characteristics, and f the polar relay PR being operated to alternately close its right-hand and left-hand contacts. With front contacts II! and I20 of relays SR2 and SRI closed and the contact members I I6 and Ill operated, recurrent impulses of current are supplied to the winding of relay SR4 through the medium of transformer T6, the current impulses flowing in the winding of relay SR4 inthe same direction so that that relay is picked up and retained energized since it is slow releasing in character. With relay SR4 picked up closing front contact I2I, the lamp I22 of signal CSI is illuminated to display a clear signal.

If approach restricting tramc conditions exist for the section W-X and the recurrent impulses of current are all of positive polarity the tube GI is periodically conductive and'relay SRI is picked up .and relay PR is operated to close its right-hand contacts only. With relay SR2 released at the end of the slow release period opening its front contact I I9 current'is removed from the primary winding of transformer T6 and the third repeater relay SR4 is deenergized and released. With relay SR4 released closing its back contact I26 and relay SRI picked up closing its front contact I24, a circuit is formed for the lamps I21 and I28 of signal CSI to display an approach restricting signal.

Under approach trafflc conditions in the section W-X, the recurrent track circuit current impulses are of negative polarity and tube G2 is periodically conductive so that relay SR2 is picked up while relay SRI is released. Relay SRI upon releasing to open front contact I29 removes current for energizing the relay SR4 and that relay is released. A circuit is now formed over back contact I26 of relay SR4, back contact I29 of relay SRI and front contact I25 of relay SR2 for the lamp I30, and signal CSI displays an approach signal. With the section WX occupied and the track circuit current shunted away from the second train so that both tubes GI and G2 remain non-conductive, the relays SRI, SR2 and SR4 are all deenergized. A circuit is now formed including back contacts I26, I29 and I3I for the lamp I32, and signal CSI displays a slow speed signal.

The train-carried apparatus of Fig. l is similar to that of Fig. 6 except the polar relay PR, transformer T6 and relay SR4 are replaced by a repeater relay SR5 which is controlled by the relay R5. The inductor LI in multiple with the winding of relay R5 is omitted and the connection of the generator 84 with the anode circuits is not controlled over a back contact of the relay R5.

When a train on which the apparatus of Fig. '7 is mounted enters the track section WX of Fig. 4 under clear traflic conditions, the recurrent track circuit current impulses alternately positive and negative in polarity cause the tubes GI and G2 to be alternately conductive in the manner previously described, and relays SRI and SR2 are picked up. With both relays SRI and SR2 picked up to close the respective front contacts I and H9, a condenser I33 is charged during the next impulse so that relay R5 is picked up to closeits front contact I34. At the end of denser over a contact of a relay picked up only during a current impulse interval and discharging such stored energy during the interval between successive current impulses to energize another relay is disclosed and claimed in my aforementioned copending application Serial No.

Under approach restricting trafllcconditions for the section W-X the tube GI' is made conductive in .response to the recurrent track circuit current impulses so that relay SRI only is picked up, and thelamps I21 and I2. of signal CSI are illuminated over back contact I39 of relay SR5 and frontcontact I24 of relay SRI to display an approach restricting signal. Under approach traillc conditions for the section W- X tube G2 only is made periodically conductive in response 'to the track circuit current impulses so that only relay SR2 is picked up. The lamp I30 of signal CSI is now illuminated over back contacts I38 and I29 of relays SR5 and SRI, respectively, and front contact I of relay SR2 so that the signal CSI displays an approach signal. In the event that the track section WX is occupied, so that no energy is induced inthe-windings 25 and 29,

are deenergized and the slow speed signal lamp I32 is illuminated over the circuit including back contacts I38, I29 and I3I.

In Fig. 8, the train-carried apparatus is the same as in Fig. 7 except the repeater relay SR5 is made slow releasing and is governed through the medium of a transformer T1 and a full wave rectifier I39, the primary 'winding I40 of transformer Tl being interposed in the anode circuits for the tubes GI and G2, as will be apparent from an inspection of Fig. 8.

When the train on which the apparatus of Fig. 8 is mounted occupies the section W-X of Fig. 4 under clear traffic conditions in advance and the recurrent track circuit current impulses alternately of positive and negative polarity cause the tubes GI and G2 to be alternately cona manner previously described. With relays SRI and SR2 picked up closing front contacts I20 and H9 the recurrent impulses of current flowing in the winding I40 of transformer T1 induce electromotive forces in the secondary winding I4I of that transformer which are rectified by rectifier I39 and supplied to the winding of relay SR5 so that relay SR5 is picked up. The relays SR5, SRI and SR2 of Fig. 8 control the operating circuits for the signal CSI in the same manner as described for Fig.- '7. It is clear, therefore, that the apparatus of Fig- 8 will respond to the different trafilc conditions produced for the track circuit for section WX of Fig. 4 in substantially the same manner as the apparatus of Fig. 'l and the description need not be repeated in detail.

In the train-carried apparatus of Fig, 9, the transformer T1, rectifier I39 and relay SR5 of Fig. 8 are replaced by a rcla-y SR6 which isprovided with slow pick-up slow release characteristics. In the form of the invention disclosed in Fig. 9 the primary winding II2 of transformer T4 and the primary winding 3' of transformer T5 are each so proportioned as to provide the desired inductance in series with condenser C I without any additional inductance. When the train on which the apparatus of Fig. 9 is mounted occupies the track section W--X of Fig. 4

under approach trafilc conditions and the track circuit is supplied with current impulses of negative polarity the tube G2 and relay SR2 are responsive in the same manner as described in connection with Fig. 7. Under approach restricting trafllc conditions and the track circuit is supplied with current impulses of positive polarity the tube GI and relay SRI are responsivethereto in substantially the same manner .then all three of the relays SRI, SR2 and SR5 as described in Fig. 7. Again, under clear traflic conditions so that the track circuit is supplied with recurrent impulses of current alternately positive and negative in polarity both tubes GI and G2 are responsive and both relays SRI and are energized. The top winding of relayv SR6 is energized over front contacts 119 and I20 of relays SR2 and SRi and the relay SR5 is picked up at the end of its slow pick-up period in response to clear traffic conditions of the track circuit. It is to be noted that the relay SHE is made slow to pick up in part by being provided with a lower winding which is shortcircuited over its own back contact I42. The

operating circuits for the signal US! are governed by the relays SR6, SBA and SR2 of Fig. 9 in a manner similar to the control effected by relays SR3 SRI and SR2 of Fig. 7, and a further description thereof is thought tobe unnecessary. It should be noted that the relay SR6 is provided with a slow to pick up period sufficient that relay SR6 is not picked up during the brief interval both relays SRI and SR2 may be energized during a change from approach restricting to approach or vice versa, and a false flash of a signal indication by the signal CSI is avoided,

In Figs. 6, 7, 8 and 9 the inductor windings 25 and '26 are independent of each other as pointed out hereinbefore. When the inductors are thus arranged only one electron tube GI or G2 could be energized in case track circuit current flows in one rail only as it may sometimes do because of a broken track rail. With only one tube GI or G2 energized only one of the restrictive indications, approach restricting or approach, can be efiected but a false clear signal cannot be effected.

Referring to Fig. 10, the track rails Id and lb are formed into consecutive insulated track sections each of which is provided with a track circuit the same as in Fig. 1. In Fig. 10 a train TC indicated diagrammatically by dotted lines is shown as occupying the section W-X.

The source of code impulses for the track circuit for the section W.-X of Fig, 10 comprises battery 2, track transformer TI and a code transmitter 0T2. The code transmitter CT? is of the frequency code type, several of such types being well known to the art. The operating winding of the code transmitter 0T2 is connected with the current source and is continuously active to operate three code contact members 151), i201) and I802), the arrangement beingsuch that the code contact member b is operated to close contact 'I5al5b at the rate of say '75 times per minute, code contact member I?) is operatedto close contact l20al20b at the rate of 120 times per minute, and the code contact member I 8012 is operated to close contact I8lla-I80b at the rate of 180 times per minute.

At such time as a relay WA of the code responsive relay means for ,the track circuit of the section next in advance of section W-X is picked up closing its front contact H3, or when relay WA is released closing its back contact I and a second relay WR of the code responsive relay means is picked up closing its front contact I45, the battery 2 is connected across the winding 4 of transformer TI over the contact I80a-I8Ub of the code transmitter GT2 and direct current impulses of the code fre- WA and WE are released closing back contacts I" and I48, respectively, and a third relay WL of the code resporfsiverelay means is picked up closing its front contact I41, the battery! is connected across winding 4 over I20a-I20b of the code transmitter CTZ and direct current impulses of the code frequency of I20 are supplied to the track circuit of section W-X, the impulses being all of positive polarity. Again, when relays WA, WR and WL are all released closing back contacts I, 6 and I48, battery 2 is connected across wlnding 4 over the code contact Ha-15b and the track circuit for the section W-X is supplied with impulses of current at the code frequency of T5, the impulses again being all of positive polarity.

Assuming for the time being that the train TC does not occupy the section WX, a code following relay X'IRI connected across the rails of the section W-X operates its contact member I49 at the code frequency of'the impulses supplied to the track circuit. Operation of the codecontact member I49 causes direct current to be alternately supplied to the two portions of the primary winding I50 of a transformer T8 with the result that electromotive forces of corresponding code frequency are induced in the secondary winding I5I of that transformer and are applied to the input terminals of a frequency decoding unit XF'D. The structure of the frequency decoding unit ZFD is immaterial, several of such decoding units being well known. It is deemed suflicient for this application to say that the decoding unit XF'D causes a relay XA connected with its output side to be energized only in response to code impulses of the 180 code frequency, causes a relay XR connected with its output side to be energized only in response to code impulses of the 120 code, and causes a relay XL connected with its output side to be energized in response to either the 180, 120 or 75 code frequency.

In like fashion. a code following relay WTRI for the track circuit of the section next in ad- .vance of section -WX governs through a transformer T9 a frequency decoding unit WFD for selectively energizing the relays WA, WR and WL in accordance with the code frequency of the impulses of the track circuit current of that section.

It should be pointed out that the code frequency of 180 for the track circuit impulses represents clear traflic conditions, the code frequency of 120 for the track circuit impulses represents approach restricting traflic conditions, the code impulse frequency of 75 for the track cIrcult impulses represents approach traflic conditions, and an absence of any of these code impulses represents stop or slow speed traflic conditions.

contact" 1 The, relays-WA, WR andWL govern the operating circuits for wayside signal WS as will be apparent from Fig. 10. Such operative circuits are shown conventionally only for the sake of simplicity, since they would be in accordance with standard practice and form no part of my present invention.

The relays XA, XR and XL for the track circuit of section W-X govern the track circuit for the section next in therear and the operating circuits for the wayside signal XS in the same manner as the relays WA, WR and WL control the track circuit of section W-X andthe operating circuits for signal WS.

It should also be pointed out that the code 1mpulses of direct current'applled to the track circuits of Fig. 10'are of relatively short duration the generator.

and relatively high peak voltage the same as in Figs. 1 and 4 except for the fact that they are all of the same polarity and have different code frequencies whereas in Figs. 1 and 4 the impulses are of the same frequency but different in polarity.

The train TC of Fig. 10 is provided with traincarried apparatus which is selectively responsive to the different code frequencies of the direct current track circuit impulses. The train TC is provided with inductor windings '25 and 26 the same as in Fig. 2. windings and 26 are connected across the primary winding I52 of an input transformer TIO, filter circuits being preferably interposed in the connection. As here shown, the filter circuits are made up of a condenser I53 connected in series with an inductor I54 and tuned to by-pass 25 cycle alternating current; and a condenser I55 connected in series with aninductor I56 and tuned to by-pass 60 cycle alternating current. By using such filter circuits interference by 25 cycle and 60 cycle alternating current flowing in the track rails is avoided.

The secondarywinding I51 of transformer TIIJ is connected across the grid I58 and filament I59 of an amplifying tube I66 of the indirect heater type. The plate circuit of tube I60 is coupled withthe grid circuit of a controlled ionization tube G3 by a well-known form of coupling circuit made up of resistors I6I and I62 and a condenser I63. MG is used to supply plate voltage for the tube I60. In this instance the tube G3 is of the indirect heater type, the two principal electrodes being anode I64 and cathode I65 while its control element is a grid I66.

The anode circuit for tube G3 includes terminal B300 of generator 84, resistor 32 top winding of a code following master relay MRI, anode I64, tube space to cathode I65 and terminal N300 of Condenser CI and inductor LI are connected with the anode circuit to provide the I tube G3 with an oscillatory circuit, this circuit involving condenser CI, top winding of relay MRI, theanode-cathode space of tube G3 and inductor LI. Normally the condenser CI is charged at substantially the voltage of the genorator 84 the same as in other forms of the invention.

The code following master relay MRI controls .a frequency decoding unit TFD of the standard type, the input side of unit TFD being connected with the secondary winding I61 of a transformer TII the two portions of the primary winding I68 of which transformer are supplied with direct current over the code contact member I69 of relay MRI. In accordance with usual practice a relay TA connected with the output side of the decoding unit TF'D is energized only when the relay MRI isoperated at the code frequency of 180 cycles per minute, relay TR is energized only when relay MRI is operated at the code frequency of 120 cycles per minute, andrelay TL is energized when the relay MRI is operated at either 180, 120 or 75 code frequency. The relays TA, TR and TL govern the operating circuits for the cab signal CSI as is obvious from Fig. 10.

Assuming that clear traflic conditions exist in the section w .x of Fig. 10 so that track circuit impulses of the code frequency of 180 are flowing in the track rails, each impulse induces an electromotive force in the train-carried windings 25 and 26 which is amplified by tube I66 and is applied to the control grid I66 of tube GI. The wave form of such induced electromotive force is similar to that illustrated in curves 1, 3, and 5 of The generator 84 of themotor generator Fig. 15, since each track circuit impulse isof direct current of relatively short duration and high peak voltage. The parts are so connected'that during the first half cycle of the induced electromotive force the grid I66 of tube G3 is rendered positive in potential with respect to the cathode I65 and tube G3 is ionized and becomes conductive. Current flows from condenser CI through the top winding of relay MRI, anodecathode space of tube G3, inductor LI and back to condenser CI. Current also flows from generator 84 through the associated anode circuit including resistor 32 and the top winding of relay MRI as well as the anode-cathode space of tube G3. When, because of the oscillatory nature of the discharge from condenser CI, the current through tubeG3 falls to a relatively low value the tube G3 deionizes and becomes non-conductive. The condenser CI is quickly recharged so that the above described operation is repeated for each code impulse of the track circuit current. The parts are so proportioned that tube G3 deionizes and condenser CI is recharged in a period slightly less than .3 second which is the interval between successive impulses of the 180 code frequency.

The impulses of current passed by tube G3 flowing in the top winding of relay MRI causes that relay to be operated at the same code frequency with the result that the relays TA and TL are energized. e

Under approach restricting traffic conditions and the track circuit current impulses are of the 120 code frequency, the operation of the train carried apparatus of Fig. 10 is similar to that described above except for the fact that relay MRI is operated at the code frequency of 120 and relays TR and TL are energized. Again, under approach traffic conditions so that the track circuit is supplied with impulses of the 75 code frequency, the operation of the train-carried ap paratus is the same except relay MRI is operated at the code frequency of 75 and relay TL is energized. Under slow speed trafiic conditions at which time the track circuit is shunted by a train in advance then relay MRI does not operate and all three relays TA, TR and TL are deenergized. It is clear therefore that the cab signal CSI of Fig. 10 is caused to display a signal correspondcoding unit TFD have nearly equal on and 01T" periods, therelay MRI is provided with a lower winding which is connected with a reactor L3 over front contact 210 and transfer contact III of ma; continuity transfer type of contact. When relay MRI is released (off position) reactor L3 is supplied with current from th'e'source B32--N32 over contacts ITO-I'll and reactor L3 stores up magnetic energy, the amount of energy depending within limits upon the length of time reactor L3 is supplied with current. When relay MRI is picked up (on position) the reactor L3 is connected with the lower winding of relay MRI and disconnected from the current source. This causes current to flow in the lower winding of relay MRI due to the decay of the magnetic energy stored in reactor L3 and relay MRI is maintained energized for an interval subsequent to the termination of the impulse of current flowing in the top winding of that relay due to the action of the tube G3. Thus the code impulses applied to decoding unit TFD due to the operation of 7 relay MRi have substantially equal "off and on periods notwithstanding the fact that relay MRi may be operated at 180, or 120 .or '75 code frequency, the oil and on" periods of relay MRI being of an interval corresponding to the code frequency.

Referring to Fig. 11, the train-carried apparatus comprises two receiving channels one effectively influenced by recurrent impulses of direct current and the other effectively influenced by coded alternating current. If the train on which the apparatus of Fig. 11 is mounted is operating over territory on which the track circuits use direct current code impulses such as provided by the trackway apparatus of Fig. 10, a receivingv channel comprising a controlled ionization type of electron tube is responsive thereto. When the train is operating over territory where track circuits are provided which use coded alternating current of 100 cycles per second such as are so widely used in present day code signalling systems, a receiving channel including a high vacuum amplifying electron tube is responsive thereto.

In Fig. 11, the receiving channel responsive to direct current impulses includes an input transformer TI2, a controlled ionization t'ube G3 and a master relay MRi, The receiving channel responsive to coded alternating current includes an input transformer TI3, a pentode tube 25L6 and a master relay MR. The inductor windings 25' and 26 of Fig. 11 are connected with the primary windings I12 and I13 of the transformers TI! and II3, respectively, in multiple. Hence energy received from the track circuit is applied to the two receiving channels of Fig. 11 in parallel.

Referring to the receiving channel including tube G3,the grid circuit of the tube is connected with the secondary winding I15 of the input transformer 'II2 as will be apparent by an inspection of the drawing. The anode circuit of tube G3 and the associated oscillatory circuit including condenser CI and inductance LI are the same as in Fig. 10. Also, the top winding of the master relay MRI is interposed in the anode and oscillatory circuits the same as in Fig, 10. It

should be noted that the lower winding of relay MRI of Fig. 11 is connected with the reactor L3 over a transfer contact of the usual type rather than over a continuity transfer contact as in Fig. 10. The reactor L3 of Fig. 11 is connected with the B32-N32 source of current over back contact I95 when relay MRI is deenergized and is transferred to the lower winding of the relay over front contact I86 when the relay is energized. A resistor I80 is connected across reactor L3 to prevent a loss of the energy stored in the reactor during a transfer of the associated contact. Relay MRI when operated causes through its contact member I59 direct current to be alternately supplied to the two portions of winding I58 of transformer TII with the result'that impulses of current of a frequency corresponding to the frequency at which the relay MRI is operated are supplied to the input terminals of the frequency decoding unit TFD. A resistor I9! is preferably connected across the supply circuit ahead of the contact member I69 to allow a substantially uniform flow of direct current through the winding I68 when relay MRI is not operated. The purpose of resistor I9! will appear hereinafter.

Relays TA, TRand TL of Fig. 11 are connected with the output side of the decoding unit TFD and are selectively governed thereby in the same.

manner as in Flg.;10. Also, the relays TA, TR

and TL govern the circuits for the cab signal CSI in the manner previously described. Hence, direct current impulses of 180, 120 and 75 code frequencies when applied to the receiving channel including tube G3 are effective to cause the signal CSI to display a corresponding signal indication.

Referring to the receiving channel including tube 25L5, a condenser IN is interposed in the connection of primary winding I13 of transformer TI3 with the windings 25 and 26, and a con-.

denser, I84 is connected across the secondary winding I16 of transformer TI3 which secondary winding is included in the grid circuit of tube 25L6 as is apparent from Fig. 11. The parts are so proportioned that the input circuit for tube L6 is effectively responsive only to alternating current of 100 cycles per second. The tube 251.6 is of the low voltage type and its plate circuit is supplied from the B32N32 source of current, plate Ill of tube 25L5 being connected with terminal B32 through primary winding H8 of a transformer TH, and cathode I19 of the tube being connected with terminal N32 through a biasing resistor I98. The secondary winding I8I of transformer TIB is connected with the winding of relay MR. Relay MR is of the usual code following type and is provided with two contact members I82 and I83 which remain in the position to which they were last moved when the relay is deenergized. Relay MR controls the supply of direct current to the winding I68 of transformer TII in a manner to shortly appear, and hence causes impulses of current to be supplied to the input side of the decoding unit TFD which are of a frequency corresponding to the frequency at which relay MR is operated. Hence alternating current of the 180, 120 and 75 code frequencies when applied to the receiving channel including tube 25L6 are amplified and decoded to control relays TA, TR and TL and in turn to cause signal CSI to display corresponding signal indications.

Assuming the train on which the apparatus of Fig. 11 is mounted is moving over the track section W-X of Fig. under clear traffic conditions so that direct current impulses of 180 code frequency are supplied to the track circuit, corresponding electromotive forces are induced In the windings 25 and 25 and are applied to the two receiving channels in parallel, the train TC of Fig. 10 being, of course, considered as not present.

Since the wave form of the electromotive force induced in windings 25 and 26 in response to the direct current impulses contain little if any alternating current energy of 100 cycles, the tube 25L6 is not affected thereby. The first half cycle of the electromotive force induced in the secondary winding I of transformer TI! of each of the direct current impulses causes the grid I55 of tube G3 to be positive in potential with respect to the cathode I55, and tube G3 ionizes and becomes conductive. Tube G3 is deionized and restored to its non-conductive condition subsequent to each such current impulse by virtue of the condenser CI and its associated oscillatory circuit in the same manner as described in previous cases, relay MRI being opbe alternately supplied to the two portions of primary winding I66 of transformer TII. This signalling or supply circuit for transformer TII can be traced from terminal B over contact member I83 in its right-hand position. primary winding I85 of a transformer TI to be later referred to, left-hand portion of winding I68 and back contact of contact member I69 or righthand portion of winding I68 and the front contact of contact member I69, and contact member I82 in its right-hand position to terminal C. It follows that current impulses corresponding in frequency to the 180 code frequencyare supplied to thedecoding unit TFD and relay TA in turn is energized to cause signal CSI to display a clear indication. Operation of the apparatus in response to direct current impulses supplied to the track circuit of section W-X of the 120 or 75 code frequency in accordance with different traffic conditions causes relay TR to be picked up at the 12,0 code frequency and signal CSI to displayapproach restricting indicawave rectifier I81 are not effective to energize.

a relay R6 whose winding is connected across the output terminals of rectifier I81 sufficiently to pick up that relay. Furthermore, the resistor I91 which allows a substantially uniform amount of direct current to flow when relay MRI is op- Y erated aids in assuring that not sufflcient energy is supplied to relay R6 to pick up the relay.

Assuming the train on which the apparatus of Fig. 11 is mounted is operating over a track circuit to which coded alternating current is supplied at the code frequency of 180, 120 or '15 according to different traffic conditions, each such code group of alternating current induces an electromotive force in the windings 25 and 26 which is applied to the two receiving channels in parallel; Trackway apparatus operative to supply such coded alternating current is well known and may be that disclosed in the United States Letters Patent No. 1,773,515, granted August 19, 1930, to C. C. Buchanan, for Railway trafllc controlling apparatus.

The electromotive force now induced in windings 25 and 26 will be applied to the grid circuit of tube 25L6 where it is amplified and applied through transformer TN to the master relay MR to operate relay MR in the Well known manner. With relay IVER. operated and relay MRI inactive direct current from the source BC is reversibly supplied to the left-hand portion 'of winding I68 of transformer TII with the result that electromotiveforces are induced in the secondary winding I61 of transformer TI I, and impulses of current .of a frequency corresponding to the code frequency at which relay MR is operative are supplied to'the decoding unit TFD. Relays TA, TR and TL are selectively controlled according to the frequency of the code impulses supplied to the unit TF1) in the manner previously pointed out with the result that signal CSI displays an indication corresponding to the code frequency of the alternating current impulses of the track circuit.

When relay MB is operated the direct current flowing in winding I65 of transformer TI5 is periodically reversed and the electromotive force induced in the secondary winding I86 of that transformer when rectified by rectifier I81 is effective to energize relay R6 sufliciently to pick up that relay, relay R6 being retained picked up from one impulse of the track circuit current to the next due to its slow release-characteristic.

Relay R6 in picking up to open its back contact I88 removes current from motor 86 of the motorv generator MG and generator 84 no longer supplies current to the anode circuit of tube G3,

with the result that the receiving channel including tube G3 becomes inactive. That is, relay R6 is operated by the receviing channel responsive to coded alternating current, and automatically renders the receiving channel responsive to direct current impulses inactive. Again it is to be noted that the tuning of the input circuit for the tube 25L6 as afl'ected bythe condensers I14 and I84 automatically desensitizes the re-' ceiving channel normally responsive to alternating current so that channel in unaffected by the direct current track circuit impulses.

In Fig. 12, the train-carried apparatus comprises two receiving channels the same .as in Fig. 11. In Fig. 12 the controlled ionization tube G3 of the receiving channel responsive to recurrent impulses of direct current is preceded by a stage. of amplification including a high vacuum electron tube GQ'I of the indirect heater type and having two diode plates I89 and I90. The grid of the preceding amplifier tube 6Q1 by a circuit 1 comprising resistors I6I and I62 and a condenser I63 similar to the coupling circuit of Fig. 10 except in Fig. 12 a resistor I 9I is interposed in the grid circuit of the tube G3 between resistor I62 and the terminal N32. The grid circuit for tube 6Q1 is connected directly with the inductor windings 25 and 26, a resistor I92 being interposed in the circuit adjacent the terminal N32 as is apparent from Fig. 12. The resistors I9I and I92 provide a desirable normal grid bias for tubes G3'and-6Q1, respectively. I

The receiving channel responsive to coded alternating current includes transformer TI3, tube 25L6 and master relay MR the same as in Fig. 11.

The master relays MR and MRI control the impulses supplied to the frequency decoding unit TFD by controlling the supply of direct current to the primary winding I68 of transformer TII in the same manner as in Fig. 11 except in Fig. 12 the transformer TI5, rectifier I81, relay R6 and resistor I91 are omitted.

In Fig. 12 the means for desensitizing the receiving channel including tube 25L6 so that it is not responsive to direct current impulses includes condensers I14 and I84 the same as 'in Fig. 11. In Fig. 12, the means for automatically circuit of tube G3 is coupled with the plate circuit desensitizing the receiving channel including tube former TI I and the resistor I9I of the grid circuit as of tube G3, and condenser I 94 is connected between a point Q in the supply circuit for transformer TII and the resistor I92 of the grid circuit of tube 6Q1. Also one side of the condenser I93 is connected with the diode plate I90 of tube 6Q1 over wire I 99, and one side of a condenser I94 is connected with diode plate I89 over a wire 206. Point P is located in the supply circuit between the contact member I 82 of relay MRand contact member I69 of relay MRI, and

lift

ra ipoint Q is located in the supply circuit between the contact member 583 of relay MR and the central terminal of winding I88 of transformer Ti [1.

When the train on whi h the apparatus of Fig. 12 is mounted operates over track circuits supplied with code impulses of direct current of different code frequencies as provided by the trackvzay apparatus on Fig. 10, the receiving channel including tube G3 and relay MRlresponsive and operates u'the same manner as described in detail in 11 except that the electromotive forces induced in windings 25 and are first ampli'" at BGZT.

When the o is operated over track; circuits to which ceded alternating current "lfercnt code frequenci is supplied, the receiving channel including t L3 and master relay MR responsive to age appe ng essentially a ter 1 is 03:21 alternating d surges ints 1? and c the c "4; are s i193 and its to tube 6Q"! where such applied umdirecclears Ni and which are or "'1 cos norma tory which *ts are I coded alternat .13 current the receiving channel normally z'espon lve to direct current ulses desensitized, en the operating over territory using tract; circuits in which direct current impulses are supplied the receiving channel normally responsive to alternating current unaffected due to the tuning of the input circuit of that receiving channel.

In Fig. 13 the train-carried apparatus is the same as in Fig. 12 except for the means used to desensitize the tubes 6Q! and G3. In Plg.,13 the diode plates lSQ and $80 of tube 6Q! are connected in a full wave rectified circuit made up of condensers Hi3 and 194 and an additional condenser ZOi, together with resistors 202, 203 and 204; Alternating current surges appearing at points P and Q when master relay MB is operating are rectified by the diode plates 89 and N0 and are effective to charge the condenser ill. The voltage across condenser 10! when thus charged adds to the normal bias voltage of tubes 6Q! and G3, and these tubes are provided with a bias of such negative potential that they can no longer operate.

It is clear, therefore, that when a train on which the apparatus of Fig. 13 is mounted oper- 3 ates over territory using track circuits supplied with coded alternating current the receiving channel including tube 25L6 and relay MB is responsive to control the cab signal 08!. And when the train operates over territory using track circuits supplied with coded direct current impulses the receiving channel including tube G3 and relay MRI is responsive to control the cab signal 05!, the operation being substantially the same as described in connection with the apparatus of Figs. 11 and 12.

It to be understood, of course, that the traincarried apparatus of any of the several forms of apparatus embodying my invention can include circuits for controlling the air brake and power equipment according to any of the well-known arre igements, if desired.

Although I have herein shown described only certain forms of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims Without deport-- lug "n the spirit and scope of my inve tion, thus described my invention. What I signal system comprising, trans of direct current of either positive polarity iegative polarity according to two differ ll,

ing conditions, a receiving circuit such signalling impulses of our two electron tubes of the having an anode, it; means for com g said control elements to receiving circuit so that a-selected one of the tubes ioniv a cathode and a control elen W.

aho l' m cans selectively controlled by the ini out time caused to flow in said A signal system comprising, transmitting means operative to selectively supply recurrent impulses ofv direct current of positive polarity or of negative polarity or alternately of positive and negative polarity, a receiving circuit for receiving such signalling impulses of current of different polarities; two electron tubes of the controlled ionization type each having an anode, a cathode and a control element; means for connecting said control elements to said receiving circuit so that a selected one of the tubes ionizos only for current impulses of positive polarity and the other tube ionizes only for current impulses of negative polarity, a source of direct current, a first and a second relay, means to connect the positive terminal of said source With the anode of one tube through a winding of said first relay and with the anode of the other tube through a winding 01' said second relay, other means to connect the negative terminal of said source with the cathode of each tube, means to connect a condenser and an inductance between the cathodes of the two tubes and the common terminal of said relay windings, said condenser normally charged from said source and discharging when at times transmitting recurrent LlTl" 

